If it's like my old 1084 (with the big square power button and flip down panel on the front) then the circuit board just floats in a channel moulded into the two halves of the case. Just wiggle things a little bit (don't touch anything on the pcb to be safe!) and the back half of the case should come free. The cable to the speakers as I remember is a little on the short side so you'll have to disconnect it to be able to lay the cover aside.
I think there is also a screw or two at the back of the cover, near the audio inputs, that needs to come out -- if you didn't take it out, it would want to pull the board out as you pull off the cover.